Earth-working implement



May 17,1966 J. FRENCH ETAL EARTHWORKING IMPLEMENT 3 Sheets-Sheet 1 Filed May '7, 1964 INVENTORS J. L. FRENCH T.C.SCHRADER 8| A.J.VAN AUWELAER BY ATTORNEY May 17, 1966 J. L. FRENCH ET Al. 3,251,491

EARTH-WORKING IMPLEMENT Filed May '7, 1964 3 Sheets-Shae; Z

INVENTORS J. L.FRENCH,T. C. SCHRA 8 A.J. VAN AUWEL WMaW ATTORNEY y 7, 1966 J. L. FRENCH ET AL 3,251,491

EARTH-WORKING IMPLEMENT Filed May 7, 1964 V 3 Sheets-Sheet 5 INVENTOR. J.L.FRENCH,T.C.SCHRADER 8:

Ad. VAN AUWELAER BYWWa-M ATTORNEY and the maximum depth of cut.

3,251,491 EARTH-WORKING IMPLEMENT v John L. French, Moline, Thomas C. Schrader, Rock Island, and Albert J. Van Auwelaer, East Moline, 111., assignors to Deere & Company, Moliue, 111., a corporation of Delaware Filed May 7, 1964, Ser. No. 365,750

16 Claims. (Cl. 214-438) This invention relates to earth-working implements and more particularly to an earth-working implement having a vertically movable boom structure carrying at its outer end a dipper stick, and the latter in turn carrying a bucket or other type of material-handling device. More particularly this invention relates to the aforementioned type of implement that utilizes an extensible and retractable dipper stick. Still more particularly this invention relates to a dipper stick extension.

Typical of an earth-working implement having a boom and a dipper stick is a backhoe. When using such an implement, there are various advantages in having an ex- -tremely long reach, i.e., the maximum distance the backhoe bucket may extend from the backhoe frame as it penetrates the ground surface. The effectiveness of a backhoe is also measured by the depth of cut'that a backhoe may reach. When designing a backhoe, there are several factors that may determine the length of the backhoe boom and the length of the backhoe dipper stick. One of these factors is the ability of the backhoe to be completely folded for transport, i.e., the boom is disposed in substantially a vertical position and the dipper stick depends from the upper end of the boom in a minimum angular realtion thereto so that the bucket is spaced from but relatively close to the ground. Therefore, one

of the problems of providing an extension on the dipper present invention to provide a dipper stick construction utilizing a dipper stick extension capable of being extended and retracted longitudinally relative to the basic dipper stick. Thedipper stick as well as the entire backhoe may, upon the extension being in its extended position relative to the dipper stick, obtain the maximum reach However, being retractable, the extension may be moved longitudinally in a retracted relation to the dipper stick when it is desired to move the backhoe in transport.

It is a further object of the present invention to pro- "vide structure permitting the hydraulic cylinders positioning the boom structure and the hydraulic cylinders positioning the dipper stick to be utilized in retracting and extending the extension on the dipper stick.

It is a further object of the invention to provide a method of retracting a dipper stick extension consisting of unlocking the extension so that it is in a condition for retraction, and positioning the boom and dipper stick so that the dipper stick is disposed substantially in a vertical position relative to the ground and the bucket on the end of the dipper stick contacts the ground. The

method of retracting the backhoe further consists of lowering the boom so that the extension is forced to retract realtive to the dipper stick and then locking the ex tension in its retracted position. Extension occurs by raising the boom when the extension is unlocked and permitting the extension to slide along the dipper stick.

Other objects and advantages of the present invention will become apparent to those skilled in the art as the nature of the invention is better understood from the United States Patent following description and as shown in the accompanying drawings.

FIG. 1 is a rear and side perspective view of a backhoe incorporating the structure of-the present invention and including a portion of a tractor.

FIG. 2 is a side and overhead perspective view of the dipper stick extension.

FIG. 3 is a side and front perspective view of the backhoe bucket and a portion of the dipper stick structure without an extension.

FIG. 4 is a view somewhat similar to FIG. 3 but showing the extension positioned between the dipper stick structure and the bucket.

FIG. 5 is a side view of the extension structure showing portions of the dipper stick and bucket.

FIG. 6 is a sectional view taken substantially along the line 6-6 of FIG. 5.

FIG. 7 is a side view of the backhoe and a portion of the tractor showing the backhoe in a position in which retraction of the extension is about to occur.

FIG. 8 is a view somewhat similar to FIG. 7 showing the extension in its retracted position.

FIGS. 9, l0 and 11 are views similar to FIGS. 4, 7 and 8 but showing a modified structure for and method of longitudinally adjusting the backhoe extension.

The backhoe is normally supported on one end of a tractor 10 and is composed of an upright main supporting frame 11 transversely disposed in relation to the tractor and having a pair of outwardly and downwardly extending stabilizer legs 12, 13. The backhoe normally has an operators station, not shown, but adjacent to a series of hydraulic control levers 14 that operate the various hydraulic units including hydraulic cylinders 19, 20 that raise and lower the stabilizer legs 12, 13. The transverse frame 11 carries an upright swivel structure 15 adapted to swing the backhoe laterally about its upright axis. Details of the swivel structure 15 are not considered important relative to the present invention other than to recognize that this feature is present in this backhoe. Should, however, more detailed information relative to the swivel structure 15 be desired, such may be had by referring to U.S. Patent 2,994,446. A fluid mani fold 16 receives fluidthrough hydraulic hoses 17 and discharges the fluid to various of thehydraulic devices on the backhoe. Should details of the manifold and its relation to the hydraulic mechanism on the backhoe be desired, such may be had by referring to U.S. Patent 3,120,897.

The swivel structure 15 carries at its forward side a horizontal pivot 21 carrying for vertical movement a forwardly extending main boom 22 having at its upper rear end a transverse pivot 23 receiving and carrying also for vertical movement, a dipper stick boom or structure, indicated in its entirety by the reference numeral 24. The opposite end of the dipper stick boom 24 carries a transverse pivot pin 25 normally extending through a pair of upright plates 27, 28 rigid with'the back plate of a material-handling device or bucket 26. The swivel structure 15 also carries an upper horizontal pivot 30 carrying an hydraulic cylinder 31 having its rod end connected to the boom 22 for'purposes of raising and lowering the boom 22 upon extension and retraction of the cylinder 31. The boom 22 carries a hydraulic cylinder 32 having its rod end connected directly to the dipper stick structure 24 so that extension and retraction of the cylinder 32 will effect vertical movement of the dipper stick structure 24.

The dipper stick structure 24 is composed of a main portion 35 that would normally be the entire dipper stick for a backhoe. The portion 35 has a pair of side plates rigidly joined and extending rearwardly from the pivot 23 to receive the dipper stick hydraulic cylinder 32. A pivot 38 is provided on this portion to receive the rear end of a bucket tilt cylinder 39. The forward part of the main portion of the dipper stick 24 is of channelconstruction having a pair of upright side walls 40, 41, an underside 42, and overside 4.3 interconnecting the side walls. The dipper stick portion 35 may be directly connected to the bucket 26 as shown in FIG. 3.

The extreme forward end of the dipper stick has an opening for receiving a pin and further has a pair of outwardly extending bosses 44, projecting outwardly from the sides 40, 41 and about the pin opening. A second pair of bosses as indicated at 46 in FIG. 3 project outwardly from the side walls 40, 41 and indicate the location of a second pin receiving opening. The bosses 44-46, as will later become apparent, serve as guide means on the side of the dipper stick 35 to accommodate longitudinal movement of a dipper stick extension 56.

The extension 50 is composed of a pair of upright side plates 51, 52 disposed alongside and on opposite sides of the dipper stick portion 35. The side plates 51, 52 are provided with inwardly projecting upper edge flanges 53, 54 disposed above the bosses 44-46. The side plates 51, 52 are cross braced by upper and lower U- shaped channels 55, 56 disposed beneath the underside 42 of the dipper stick portion The vertical leg portions of the lower U-shaped channel 56 are welded to the vertical leg portions of the upper channel 55 and together the channels 55, 56 form a box-like channel beneath the dipper stick portion 35. The upper U-shaped channel 55 has outwardly projecting flanges 57, 58 having their outer edges welded to the inner surfaces of the side plates 51, 52. The flanges 57, 58 are normally disposed closely to and beneath the bosses 44-46. As may be seen from viewing FIG. 6, the flanges 53, 57 and the flanges 54, 58 form tracks disposed above and below the respective bosses on the dipper stick portion 35 that permit longitudinal movement of the extension 50 relative to the dipper stick portion 35. The flanges 53, 54 are rigidly interconnected at their extreme forward end by an overhead plate 59 having a forward depending flange 60 extending between the side plates 51, 52. The plate 59 and flange 6t) serve as a reinforcing or structural member rigidifying the forward end of the extension 50. A pair of brackets 61, 62 are welded to the internal surfaces of the side walls 51, 52 and project outwardly beyond the depending flange 60. The brackets 61, 62 have transversely alined holes for receiving a pivot pin, normally the pivot pin 25, that connects the forward end of the dipper stick structure to the bucket plates 27, 23.

The side plates 51, 52 are provided with four longitudinally spaced and alined holes as indicated by the forward hole 65 and in their location by three longitudinally spaced and outwardly projecting bosses 66, 67, 68 that surround respective holes in the respective plates.

The forward hole 65 receives a transverse pivot pin 70 connecting the lower end of a link, as indicated in its entirely by the reference numeral 71, composed of a pair of arms 72, 73 lying adjacent the side plates 51, 52. Spaced longitudinally from the first link 71 is a second link 75, composed of a pair of arms 76, 77 disposed on opposite sides of the side plates 51, 52 and pivotally mounted on the extension 50 by means of a transversely extending pin 78'that extends through the side walls of the lower channel 56. The upper ends of the arms 72, 73 and 76, 77 are interconnected by a connecting link 80, the specific connecting means being by transverse pivot pins 81, 82 respectively. The pin 82 is further adapted for connection to the rod end of the hydraulic cylinder 39. The pin 81 pivotally receives a bucket link 83 composed of a pair of parallel arms 84, 85. The opposite ends of the arms 84, 85 are pivotally mounted to the bucket plates 27, 28. When the extension attachment 5!) is not attached, the link 71 may be directly connected to the dipper stick portion 35 by the pin '70, a suitable 4 opening 86 (FIG. 5), being provided at the end of the dipper stick to receive the pin 70. The pin 81 is utilized to interconnect the links 71, 83 and the rod end of the piston 39.

As may be clearly evident from viewing FIGS. 1, 5, 7 and 8 the length of the links 71, and and the respective location of the pivot pins 70, 78, 81 and 82 create substantially a parallelogram with the dipper stick portion 35. This is particularly important since it is necessary to transfer the movement of the bucket tilt cylinder 39 through the parallel linkage and to the bucket. The linkage will effect a straight line movement from the cylinder 39 to the bucket substantially axially coextensive with the rod or axis of the hydraulic cylinder 39.

Referring now to FIGS. 7 and 8 for explaining the method of operation of the invention, it should be recognized that with the extension on the dipper stick portion 35, the bucket 26 will be either in contact with the ground or closely adjacent to the ground when the backhoe is moved into a transport position. For purposes of balance, the desired transport position is one in which the boom 22 is at its maximum upright position and the dipper stick structure 24 is closely adjacent to the boom. From viewing FIG. 7 it becomes apparent the bucket 26 would come closely adjacent the ground when approaching transport and should movement of the implement occur at this time, the bucket would contact objects on the ground and damage could occur to the bucket or to other portions of the backhoe. Therefore, it is desirable to retract the extension 50 for purposes of transporting the backhoe on the tractor It From a position shown in FIG. 7, such may be done by operating the boom cylinder 31 and dipper stick cylinder 32 to move the boom and dipper stick to positions in which the dipper stick 35 is substantially vertical and the bucket is in contact with the ground. The pins 90, 91 are then removed and the entire extension 50 is in a position to move longitudinally on the dipper stick portion 35 and to be guided by the flanges 53, 57 and 54, 58 contacting the boss portions44-46. By extending the boom cylinder 31 to lower the boom 22, the bucket 26 will force retraction of the extension 50 lengthwise of the dipper stick portion 35. At the same time that retraction occurs, it will be necessary to retract the bucket cylinder 39 to permit the links 71, 75 to remain substantially in the same angular relation to the bucket 26. Upon the boss portion 67 moving into registry with the boss portions 46 of the backhoe extension 35, the pin 91 may be extended through the side plates 51, 52 and the backhoe dipper stick portion 35 and the entire extension 50 will be held in its retracted position. To extend the extension 50, the backhoe may be moved into the position shown in FIG. 8, the pin 91 removed and the boom 22 raised until the extension 50 is in its extended position. The pins 90, 91 may then be placed in the proper alined holes.

It should be recognized that other methods of retracting the extension 50 on the dipper stick portion 35 may be utilized. However, all methods will include the application of some force on the dipper stick portion 35 while the bucket 26 is bearing against an immovable object. The force may be applied by any of a number of the hydraulic cylinders on the backhoe, or, the force may be applied by the power source of the tractor by placing the bucket 26 against an object while the dipper stick is placed substantially horizontal and driving the tractor toward the bucket.

In the modified form of the invention shown in FIGS. 9-11, substantially identical structure is used and consequently similar numbers are used to denote similar structure.

In the modified form of the invention and for purposes of moving the extension 50 longitudinally, and particularly to its retracted position, a pin 95 is inserted in the boss 67 and projects outwardly sufficient to be disposed as an abutment in the path of swing of the link 75. The pin 95 may or may not be one of the pins removed from the connections between the extension structure 50 and the dipper stick 35.

Referring now to FIGS. and 11, the operation of retracting the extension 50 is by retracting the cylinder 39 until the link 75 contacts the abutment rod 95. The pins 90, 91 may then be removed. Further retraction of the cylinder 39 will then force the extension 50 to retract on the dipper stick 35 until boss 67 is aligned with boss 46 on the dipper stick and as shown in FIG. 11. The pin 95 may then be forced into the boss 46 into the opening of the boss 46 to thereby lock the unit in retracted position.

If it is desired to use one of the pins 90, 91 as the abutment pin it will be necessary to drop the bucket to the ground and remove the pins and place one in the boss 67. Then the cylinder 39 may be retracted in the manner previously described.

If it is desired to force extension of the extension structure 50, the pin 95 may be placed in an opening on the bucket side of the link 75. Extension of the cylinder 39 would then force extension.

It should be recognized that other forms and variations of the present invention will occur to those skilled in the art following review of the present disclosure. Therefore, while the present forms and methods were shown in detailed manner for the purpose of clearly and concisely illustrating the principles of the invention, it should be recognized that there was no intention to limit or narrow the invention beyond the broad concepts set forth in the appended claims.

What is claimed is:

1. On a backhoe including a frame, a boom pivoted for vertical movement on the frame, a dipper stick including a main portion pivoted on the end of the boom for vertical movement and an extension supported on the portion for longitudinal. movement relative thereto between extended and retracted positions, power means for effecting vertical movement of the boom and dipper stick about the pivots, detachable locking means for retaining the extension in the extended and retracted positions, and a material handling device on the end of the extension, the improvement residing in a method of retracting the extension from its extended position comprising: positioning the boom and dipper stick whereby the dipper stick is vertically disposed and the material handling device engages a comparatively immovable surface; removing the detachable locking means between the main portion and extension on the dipper stick; lowering the boom to force retraction of the extension; and locking the extension in its retracted position.

2. On a backhoe including a frame, a boom pivoted for vertical movement on the frame, a dipper stick including a main portion pivoted on the end of the boom 'for vertical movement and an extension supported on the comprising: positioning the boom and dipper stick whereby the dipper stick is vertically disposed and the material handling device is closely adjacent a comparatively im movable surface; removingthe detachable locking means between the main portion and extension on the dipper stick; selectively lowering the boom to force retraction of the extension and raising the boom to cause extension; and locking the extension in its relocated position.

3. On a backhoe including a frame, a boom pivoted for vertical movement on the frame, a dipper stick including a main portion pivoted on the end of the boom for vertical movement and an extension supported on the portion for longitudinal movement relative thereto between extended and retracted positions, power means for effecting adjustment of the boom and dipper stick about the pivots, detachable locking means for retaining the extension in the extended and retracted positions, and a ,per stick; selectively adjusting the power means to extend or retract the extension; and locking the extension in its relocated position.

4. An extension for a dipper stick having a channel construction with a pair of oppositely disposed vertical sides and an underside and a horizontal pivot at its end with outwardly projecting boss portions adjacent the end and projecting from the respective sides, the extension comprising: an elongated structure including a pair of parallel upright longitudinally extending plate elements disposed alongside and outwardly of the respective sides and rigidly interconnected by laterally disposed structure beneath the underside of the dipper stick; longitudinally extending track means on the inner surfaces of the plate elements adapted for cooperation with the boss portions whereby the structure may move and be guided longitudinally of the dipper stick; means on the structure for interlocking the dipper stick and elongated structure in extended and retracted positions relative to one another; a pair of longitudinally spaced apart and substantially parallel links pivotally connected at lower ends to the structure; a link interconnecting the upper ends of the aforesaid links and forming with the latter end the elongated structure substantially a parallelogram type linkage, and means at the upper end of one of the links adapted for operative connection to a hydraulic power unit; and means at the upper end of the other link adapted for operative connection to a material carrying device.

5. An extension for a dipper stick having oppositely disposed vertical sides with outwardly projecting guide portions projecting from the respective sides, the extension comprising: an elongated structure including a pair of longitudinally extending plate elements disposed alongside and outwardly of the respective sides rigidly interconnected; longitudinally extending track means on the inner surfaces of the plate elements adapted for cooperation with the guide portions whereby the structure may move and be guided longitudinally of the dipper stick; means on the structure for interlocking the dipper stick and elongated structure in extended and retracted positions relative to one another; a pair of longitudinally spaced apart and substantially parallel links pivotally con nected at lower ends to the structure; a link interconnecting the upper ends of the aforesaid links and forming with the latter and the elongated structure substantially a parallelogram type linkage, and means at the upper end of one of the links adapted for operative connection to a hydraulic power unit; and means at the upper end of the other link adapted for operative connection to a material carrying device.

6. An extension attachment for a backhoe boom of rectangularcross section and having oppositelydisposed vertical sidesand pin receiving openings in the sides with boss portions formed about the openings projecting outwardly from the respective sides, the extension attachment comprising: an elongated structure including a pair of' rigidly interconnected longitudinally extending plate elements disposed alongside and outwardly of the respective sides; pin openings in the plate elements; guide means on the inner surfaces of the plate elements adapted for cooperation with the boss portions whereby the structure may move and be guided longitudinally of the boom; and detachable pin means on the structure adapted to seat in the pin receiving openings and pin openings for interlocking the boom and elongated structure in an extended position.

7. A dipper stick structure comprising; a main elongated portion of channel construction with a horizontal pivot at its end with outwardly projecting boss portions adjacent the end projecting outwardly from opposite sides: an elongated extension structure including a pair of upright longitudinally extending plate elements rigidly joined and disposed alongside and outwardly of the respective sides; longitudinally extending track means on the inner surfaces of the plate elements adapted for cooperation with the boss portions whereby the structure may move and be guided longitudinally of the main portion; means for interlocking the main portion and extension structure in extended and retracted positions relative to one another; a pair of longitudinally spaced apart and substantially parallel links pivotally connected at lower ends to the structure; a link interconnecting the upper ends of the aforesaid links, and means at the upper end of the links adapted for operative connection to a hydraulic power unit; and means at the upper end of the other link adapted for operative connection to a material carrying device.

8. A dipper stick structure comprising: a main elongated portion of channel construction with a horizontal pivot at its end with outwardly projecting boss portions adjacent the end projecting outwardly from opposite sides; an elongated extension structure including a pair of upright longitudinally extending plate elements rigidly joined and disposed alongside and outwardly of the respective sides; longitudinally extending track means on the inner surfaces of the plate elements adapted for cooperation with the boss portions whereby the structure may move and be guided longitudinally of the main portion; and means for interlocking the main portion and extension structure in extended and retracted positions relative to one another.

9. A dipper stick structure comprising: a main elongated portion of channel construction with a plurality of horizontal pin receiving openings with outwardly projecting boss portions adjacent the openings projecting outwardly from opposite sides; an elongated extension structure including a pair of upright longitudinally extending plate elements rigidly joined and disposed alongside and outwardly of the respective sides; longitudinally extending track means on the inner surfaces of the plate elements adapted for cooperation with the boss portions whereby the structure may move and be guided longitudinally of the main portion between extended and retracted positions; pin openings in the elongated extension structure adapted for registry with the pin receiving openings of the main portion when in extended and retracted positions; and removable pin means adapted for insertion in the openings when in registry.

10. A boom structure comprising: a main elongated portion of rectangular-shaped channel construction with a plurality of horizontal pin receiving openings and having opposite upright sides; an elongated extension structure including a pair of upright longitudinally extending plate elements rigidly joined and disposed alongside and outwardly of the respective sides; longitudinally extending track and guide means between the upright sides and the plate element-s adapted for cooperation whereby the extension structure may tmove and be guided longitudinally of the main portion between extended and retracted positions; pin openings in the elongated extension structure adapted for registry with the pin receiving openings of the main portion when in extended and retracted positions; and removable pin means adapted for insertion in the openings when in registry.

11. An extension for a dipper stick, the dipper stiok having a channel construction with a pair of oppositely disposed vertical sides and an underside and a horizontal pivot at its end with. outwardly projecting boss portions adjacent the pivot and projecting from the respective sides, the extension comprising: an elongated structure including .a pair of parallel upright longitudinally extend- .ing plate elements disposed alongside and outwardly of the respective sides and rigidly interconnected by laterally disposed structure beneath the underside of the dipper stick; longitudinally extending track means on the inner surfaces of the plate elments adapted for cooperation with the boss portions whereby the structure may move and be guided longitudinally of the dipper stick; means on the structure for interlocking the dipper stick and extension structure in extended and retracted positions relative to one another; two pair of longitudinally spaced apart and substantially parallel links pivotally connected at lower ends .to the structure; a link interconnecting the upper ends of the aforesaid links, and means at the upper end of the links adapted for operative connection to a hydraulic .power unit; means at the upper end of the other link adapted for operative connection to a materialcarrying device; and an abutment element on the structure adapted for positioning in the path of movement of at least one of the links whereby when in contact with the link, the hydraulic unit is capable of retracting the structure to its retracted position.

12. An extension for a dipper stick, the dipper stick having a channel construction with a pair of oppositely disposed vertical side-s and an underside and a horizontal pivot at its end with outwardly projecting boss portions adjacent the pivot and projecting from the respective sides, the extension comprising: an elongated structure including a pair of parallel upright longitudinally extending plate elements disposed alongside and outwardly of the respective sides and rigidly interconnected by laterally disposed structure beneath the underside of the dipper stick; longitudinally extending track means on the inner surfaces of the plate elements adapted for cooperation with they boss portions whereby the structure may move and be guided longitudinally of the dipper stick; means on the structure for selectively interlocking the dipper stick and extension structure in extended and retracted positions relative to one another; vertical link means pivotally connected at its lower end to the structure; means at the upper end of the link means adapted for operativeoonnection to a hydraulic power unit and to a material carrying device; and an abutment element on the structure and adapted for positioning in the path of movement of the link means whereby when in contact therewith, the hydraulic unit is capable of retracting the structure to its retracted position.

13. A dipper stick comprising an elongated channel; an elongated extension structure on the channel; longitudinally extending track and guide means between the extension structure and channel whereby the structure may move and be guided longitudinally of the channel; means on the structure for selectively interlocking the channel and extension structure in extended and retracted positions relative to one another; vertical link means pivotally connected at its lower end to the structure; means at the upper end of the link means adapted for operative connection to a hydraulic power unit and to a materialcarrying device; and an abutment element on the structure adapted for positioning in the path of movement of the link means whereby when in contact therewith, the hydraulic unit is capable of moving the structure longitudinally.

14. A dipper stick comprising an elongated channel; an elongated extension structure longitudinally movable in respect to the channel; means for selectively interlocking the channel and extension structure in extended and retracted positions relative to one another; vertical link means pivotally connected at one end to the structure; means on the link means adapted for operative connection to a hydraulic power unit and to a material carrying device; and an abutment element on the structure adapted for positioning in the path of movement of the link means whereby when in contact therewith, the hydraulic unit is capable of moving the structure longitudinally in respect to the channel.

15. On a backhoe a method of adjusting the eifective length of a telescoping two-member boom construction interlocked by locking means, the backhoe includinga frame, a main :boom pivoted at one end for movement on the frame and at the opposite end to a dipper stick boom, one of .the latter booms being of the aforesaid telescoping two-member boom construction, a material handling device pivoted on the end of the dipper stick boom, and power means for effecting pivoting of the main boom, dipper stick boom, and material handling device, the method com-prising: positioning the main boom and dipper stick boom whereby the material handling device bears against a comparatively immovable surface; unlocking the locking means between the two members of the twomem'ber boom; adjusting the power means to eifect longitudinal adjustment in length of the two-member boom; and relocking the locking means to prevent further longitudinal adjustment.

16. A boom structure comprising: a main elongated portion of channel construction with horizontal pin receiving openings and boss portions formed about the openings and projecting outwardly from opposite sides of the structure; an elongated extension structure including a pair of longitudinally extending plate elements rigid- 10 ly joined and disposed alongside and outwardly of the opposite sides of the main portion; longitudinally extending guide means between the boss portions and the plate elements adapted for cooperation whereby the extension structure may move and be guided longitudinally of the man portion on the boss portions between extended and retracted positions; pin openings in the elongated extension structure adapted for registry with the pin receiving openings of the main portion; and removable pin means adapted for insertion in the openings when in registry and for preventing relative longitudinal movement between the main portion and extension structure.

References Cited by the Examiner UNITED STATES PATENTS HUGO O. SCHULZ, Primary Examiner. 

1. ON A BACKHOE INCLUDING A FRAME, A BOOM PIVOTED FOR VERTICAL MOVEMENT ON THE FRAME, A DIPPER STICK INCLUDING A MAIN PORTION PIVOTED ON THE END OF THE BOOM FOR VERTICAL MOVEMENT AND AN EXTENSION SUPPORTED ON THE PORTION FOR LONGITUDINAL MOVEMENT RELATIVE THERETO BETWEEN EXTENDED AND RETRACTED POSITION, POWER MEANS FOR EFFECTING VERTICAL MOVEMENT OF THE BOOM AND DIPPER STICK ABOUT THE PIVOTS, DETACHABLE LOCKING MEANS FOR RETAINING THE EXTENSION IN THE EXTENDED AND RETRACTED POSITIONS, AND A MATERIAL HANDLING DEVICE ON THE END OF THE EXTENSION, THE IMPROVEMENT RESIDING IN A METHOD OF RETRACTING THE EXTENSION FROM ITS EXTENDED POSITION COMPRISING: POSITIONING THE BOOM AND DIPPER STICK WHEREBY THE DIPPER STICK IS VERTICALLY DISPOSED AND THE MATERIAL HANDLING DEVICE ENGAGES A COMPARATIVELY IMMOVABLE SURFACE; REMOVING THE DETACHABLE LOCKING MEANS BETWEEN THE MAIN PORTION AND EXTENSION ON THE DIPPER STICK; LOWERING THE BOOM TO FORCE RETRACTION OF THE EXTENSION; AND LOCKING THE EXTENSION IN ITS RETRACTED POSITION. 